In the processing of coffee, typically the first step is to subject green coffee beans to a roasting process. This process causes thermal decomposition and chemical changes within the beans at which time the familiar aroma and flavour development occurs. A by-product of the roasting process is carbon dioxide gas. Following roasting, coffee almost immediately begins to release carbon dioxide. When in the whole bean state the release of carbon dioxide gas is relatively slow. In some cases it may take in excess of two weeks for all internal carbon dioxide gas built up during the roasting process to be released. In contrast, grinding coffee beans to produce ground roasted coffee results in the release of carbon dioxide and volatile aromatics over a much shortened time frame.
As a result of the discharge of carbon dioxide gas, tightly packaged coffee that has not been sufficiently degassed can cause an undesired expansion (and in some cases rupture) of packaging materials. For that reason both roasted coffee beans and ground roasted coffee are commonly transported and stored in bins or open containers following the roasting/grinding process where they are allowed to degas for anywhere from a few hours to upwards of one to two days so that the product that is eventually packaged is essentially carbon dioxide free.
Ground roasted coffee also readily absorbs atmospheric moisture and is a good desiccant. In addition, whether it be whole bean or ground, roasted coffee oxidizes when it comes into contact with air, resulting in increased levels of acidity and a general degradation in taste. For these reasons, after being sufficiently degassed coffee is often vacuum packaged in a tightly sealed container to avoid continued contact with air. Alternately, coffee is sometimes packaged in a nitrogen filled container in order to avoid oxidation through contact with air.
Unfortunately, the above described methods of processing roasted coffee suffer from a number of substantial draw backs that affect the flavour and aroma of the coffee, and ultimately its price and desirability to consumers. First, degassing coffee increases exposure of the coffee to air and results in enhanced oxidation. Commonly used bulk handling techniques further exasperate the oxidation problem by increasing the contact of the roasted coffee with air. In addition, typical bulk handling equipment that is used in coffee processing (for example conveyor belts, screw conveyors, air conveyors etc.) have a tendency to separate fine and coarse particles and can result in an uneven mixing of fine and coarse particles within individual packaged portions. Ground coffee that is allowed to come into contact with air for any extended length of time runs the risk of absorbing moisture from the atmosphere causing a reduction in the quality of the coffee.
It has also been found that a substantial portion of the aromatics associated with roasted coffee are stripped off from either the whole bean or the ground product when the carbon dioxide liberated from the coffee is removed. Appreciating that a significant loss of the aromatics from roasted coffee results in a degradation of the coffee's flavour and taste, others have developed elaborate systems that attempt to capture volatile aromatics, and later condense and process them for use in the production of instant coffee crystals.
Finally, a further limitation associated with current coffee processing methods concerns the common practice of vacuum packaging coffee. Where coffee has been packaged within a container under a vacuum environment, immediately upon opening the container the coffee is instantly, and forcefully, aerated causing enhanced and accelerated oxidation.
There is therefore a need for an improved method of processing roasted coffee that addresses a number of the limitations present in such methods as are currently in use.